The .NET 3.0, 3.5 and 3.5 SP1 releases contain just additional assemblies, added to the .NET 2.0 CLR and core assemblies. You can check if you have 3.5 dependencies by looking through the assemblies listed in the References node of your project. That node is hidden in the VB.NET IDE, click the Show All Files icon in the Solution Explorer window to see it.
Look at the Version property in the Properties window. If it says 3.0.0.0 or 3.5.0.0 then you have a dependency on a later release of .NET. Another trick is Project + Properties, Compile tab, scroll down, Advanced Compile Options, Target framework = 2.0. That will put a warning icon on references in your project that are not available in the 2.0 release.